首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3427篇
  免费   244篇
  2023年   16篇
  2022年   55篇
  2021年   101篇
  2020年   46篇
  2019年   61篇
  2018年   93篇
  2017年   74篇
  2016年   121篇
  2015年   203篇
  2014年   214篇
  2013年   269篇
  2012年   311篇
  2011年   301篇
  2010年   195篇
  2009年   158篇
  2008年   229篇
  2007年   220篇
  2006年   184篇
  2005年   171篇
  2004年   158篇
  2003年   158篇
  2002年   131篇
  2001年   20篇
  2000年   14篇
  1999年   12篇
  1998年   26篇
  1997年   16篇
  1996年   18篇
  1995年   6篇
  1994年   12篇
  1993年   9篇
  1992年   7篇
  1991年   4篇
  1990年   11篇
  1989年   6篇
  1988年   3篇
  1987年   4篇
  1986年   3篇
  1985年   2篇
  1984年   6篇
  1982年   5篇
  1981年   4篇
  1980年   6篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1966年   1篇
  1964年   1篇
排序方式: 共有3671条查询结果,搜索用时 359 毫秒
101.
Mats of the green alga Trentepohlia, a genus widely distributed in the tropics as well as temperate regions, have always been perceived as homogeneous (i.e., formed by only one species). As such, their general nature and specific feature play a supportive role in the species delimitation. However, the presence of morphologically dissimilar thalli was observed under the light microscope and when cultivating a piece of a single mat. To address this, we performed DNA cloning of the rbcL gene on mat fragments of T. abietina, T. annulata, T. jolithus and T. umbrina sampled in Europe to reveal if they are composed of one or more species. We revealed that more Trentepohlia haplotypes may coexist in a single mat. In consideration of this, we conclude that the use of material isolated in unialgal culture will be almost mandatory for a taxonomic reassessment of this complicated genus. Another direct implication of this problem is that herbarium specimens consisting of field‐collected material should not be used for direct sequencing. We further hypothesize the reasons why multiple haplotypes of Trentepohlia occur more frequently in the tuft‐like mats. Possibly, fragments and/or cells of other microalgae, including other species of Trentepohlia, might be retained in such mats more easily than in the crustose trentepohlialean mats.  相似文献   
102.
Carvalho  Fabio  Brown  Kerry A.  Waller  Martyn P.  Boom  Arnoud 《Plant and Soil》2019,441(1-2):331-347
Plant and Soil - Trade-offs between slow and fast nutrient turnover rates among plants may affect soil properties and biomass production. We examined how plant traits interact with abiotic...  相似文献   
103.
Plant Molecular Biology - Iron and phosphorus are abundant elements in soils but poorly available for plant nutrition. The availability of these two nutrients represents a major constraint for...  相似文献   
104.
The present study aims to characterize and compare the diet of bigeye and yellowfin tunas caught on aggregated schools in the western equatorial Atlantic Ocean. The samples were collected from January 2011 to June 2016. The tunas were measured on board and the stomachs were removed after evisceration. The stomachs were analyzed regarding their Index of Fullness and the importance of each prey in the diet was estimated by the Index of Relative Importance (IRI). The diet overlap was assessed by the Morisita‐Horn's Index, Non‐Metric Multidimensional Scale (NMDS), and Analysis of Similarity (ANOSIM). The feeding strategy was determined by the Costello's Diagram. The 195 bigeye and 212 yellowfin tunas ranged in fork length from 51 to 137 cm and 43 to 174 cm, respectively. The diet of bigeye tuna was composed of 10 families of fish, three cephalopod families, and four crustacean orders. The diet of yellowfin tuna was composed of 11 families of fish, three cephalopod families, and three crustacean orders. The yellowfin tuna seems to feed upon more abundant prey species near the surface like flying fish, which have the concentration enhanced by the light attractors on the boat, and occasionally on other prey from deeper habitats like lanternfish, squids, and pomfret. Bigeye tuna feed mainly at prey that commonly occurs in deeper habitats like squids, drift fish, lanternfish, and pomfret.  相似文献   
105.
106.
107.
108.
109.
110.

Introduction:

Prison population is affected by tuberculosis (TB) due to prison overcrowding. This situation reflects an inequity in health, understood as an unfair and avoidable difference between individuals and populations.

Objective:

To estimate the conditions of prison overcrowding as health inequity in prison population suffering from TB in Colombia during 2018.

Materials and methods:

This is an ecological study to estimate inequities at the national level in prison population through the use of the World Health Organization methodology for the measurement of inequalities. Based on data from the public health surveillance system, the incidence of TB was taken as an indicator and the percentage of overcrowding as an equity stratifier. Simple and complex measures of inequality were calculated.

Results:

The relative inequality between the lowest and highest quintiles of crowding showed that TB incidence among prison population with the highest crowding was 1.92 times that of the group with the lowest crowding. The inequality index identified an excess of 724 TB cases per 100,000 among those with the highest concentration of overcrowding. The health concentration index was -0.121, which shows that the incidence was concentrated in the group with the most overpopulation.

Conclusion:

In Colombia, prison population in overcrowded conditions and suffering from TB has to face unfair and avoidable inequalities as compared with those not living in these conditions. Policies are required to reduce overcrowding and improve living conditions in prisons.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号